Due to some languages using the "nplurals=1; plural=0" plural form,
and the string already in use in src/gui/calendar-management/gcal-new-calendar-page.c
with g_dngettext, add context to the other "Add Calendar" strings to fix the problem.
AFAIK, other locales (confirmed: be_BY, fa_IR, id_ID, kk_KZ, ko_KR, my_MM, zh_CN)
are also affected by this issue.